Attempting to unload a framebuffer module calls unregister_framebuffer()
which in turn gets fbcon to release it. If fbcon has no framebuffers
linked to a console, it will also unbind itself from the console driver.
However, if fbcon never registered itself as a console driver, the unbind
will fail causing the framebuffer device entry to persist. In most cases
this failure will result in an oops when attempting to access the now
non-existent device.

This patch ensures that the fbcon unbind request will succeed even if a
bind was never done. It tracks if a successful bind ever occurred & will
only attempt to unbind if needed. If there never was a bind, it simply
returns with no error.